It's only happening for the unsubscribe field...and we don't have many other applications connected. There are a total of about 15, and most of them are SalesForce apps, not 3rd party apps.
The others (non-SFDC) apps we've got are:
Ant Migration Tool
Chatter Desktop
Chatter Mobile for BlackBerry
Dataloader Bulk
Dataloader Partner
Workbench
Have any of those given you trouble in the past?